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Po‐Poster ‐ 04: A daily quality assurance measurement for dynamic MLC treatments
Author(s) -
Furutani K,
Akhtar A,
Dahl R,
Harms T
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2030983
Subject(s) - multileaf collimator , isocenter , quality assurance , collimated light , dosimetry , collimator , computer science , optics , materials science , beam (structure) , nuclear medicine , linear particle accelerator , physics , engineering , medicine , laser , external quality assessment , imaging phantom , operations management
A daily test was developed to assure intensity modulated fields are delivered with a high degree of accuracy and precision using the dynamic multileaf collimator delivery mode. Quality assurance of the MLC, particularly for dynamic mode of delivery, requires positional accuracy of individual leafs, as well as gap width defined by opposing leaf pairs. The daily test was designed to be quick, simple to use, and easy to analyze. With the secondary collimating jaws at 25 cm wide and 39 cm long, a 5mm sliding gap over 5 cm at isocenter placed between two static fields 4 cm off axis was measured dosimetrically using Kodak XV film. The sliding gap allows us to test dosimetrically the positional accuracy defined by Varian in motor encoder counts, as a function of beam on time. The speed of the leaves is controlled by the MUs delivered. Relative film dosimetry with respect to a baseline film obtained after MLC alinment is performed daily and analyzed using RIT software. In order to facilitate the registration of the QA film to the baseline film, a mounting device utilizing the upper wedge block was used. The QA test was tested using beam shaper files with controlled errors introduced and dose differences of 5% are easily detected. In addition to the daily film QA, as part of morning photon output checks a sliding gap output is measured and these results will be presented as well.